Indeed, this is what we are told by Tertullian in his commentary on this text by Marcion.
Here the evidence:
Unfortunately there is no available translation let alone a reconstruction of the antitheses available. Harnack tried to put together the material of what was in the antitheses which is not too difficult to extract, as Tertullian in his commentary on Marcion's New Testament proceeds in order. He first, in book IV of Against Marcion, gives a commentary on the antitheses (book IV 1- IV 7), from IV 8 to the end he comments on Marcion's Gospel, book V is dedicated to Marcion's Apostolos.
Now in the section of his commentary on the antitheses, we find the following entry, soon in IV 3,2: Sed enim Marcion nactus epistulam Pauli ad Galatas, etiam ipsos apostolos suggillantis ut non recto pede incedentes ad veritatem evangelii, simul et accusantis pseudapostolos quosdam pervertentes evangelium Christi (cf. Gal. 2:14), connititur ad destruendum statum eorum evangeliorum quae propria et sub apostolorum nomine eduntur, vel etiam apostolicorum, ut scilicet fidem quam illis adimit suo conferat.
Evans translates this section as follows: "But Marcion has got hold of Paul's epistle to the Galatians, in which he rebukes even the apostles themselves for not walking uprightly according to the truth of the gospel (cf. Gal. 2:14), and accuses also certain false apostles of perverting thegospel of Christ: and on this ground Marcion strives hard to overthrow the credit of those gospels which are the apostles' own and are published under their names, or even the names of apostolic men, with the intention no doubt of conferring on his own gospel the repute which he takes away from those others."
We can take from this passage that in the antitheses Marcion refers to *Galatians and reads this as a criticism of "False-Apostles". He applies this pauline critique to "those gospels". Tertullian, of course, sees "these gospels" as being "the apostle's own", "published under their names, or even the names of apostolic men": "under the apostle's names" = Matthew and John, "the names of apostolic men" = Mark and Luke. The repute that Tertullian credits to these four gospels, namely to be the first ones, to be genuine ones, Marcion credits to "his own gospel" which Marcion reckons to be "the gospel of Christ", while these four other gospels he sees as "pervertings" of it.
What is meant by this perversion is explained a little later in the antitheses, as Tertullian reports in IV 4: et nostrum ante videatur falsum quam habuerit de veritate materiam, et Marcionis ante credatur aemulationem a nostro expertum quam et editum
Evans: ours should be taken to have been false before it had from the truth material, and Marcion's be believed to have suffered hostility from ours before it [= Marcion’s] was even published
Tertullian, a little before this (IV 3), reports that Marcion spoke of his gospel that has suffered from "adulteros" (Evans: "adulterators"), from "ut cataclysmo quodam, ita inundatione falsariorum" (Evans: "a flood of falsifiers as though by some deluge").
Tertullian, hence, states in commenting on the antitheses: The four mentioned gospels are rogue ones, false ones, unless it has material from the true one, Marcion's. This true one has suffered hostility = cometition, plagiarism, rivalry, imitation. Just a sentence earlier, Tertullian paralleled: "res" vs "passio" = Evans: "an object in existence" vs "what has been done to this object"; and "materia" vs "aemulatio" = Evans: "what something is in itself" vs "opposition".
(aemulatio, better translation would be: contention or plagiarism, as Lewis & Short give: In a bad sense, jealousy, envy, malevolence, δυσζηλία: “aemulatio vitiosa, quae rivalitati similis est,” Cic. Tusc. 4, 26, 56: “infensa,” Tac. A. 13, 19: “municipalis,” id. H. 3, 57: “adversariorum,” Suet. Ner. 23; cf. id. 33: “aemulatio nasci tur ex conjunctione, alitur aequalitate, exardescit invidiā, cujus finis est odium,” Plin. Pan. 84 al.: ad aemulationem eum provocaverunt, to jealousy (said of God), Vulg. Psa. 77, 58. contentiones, aemulationes, rivalries, ib. 2 Cor, 12, 20).