This was covered in the paragraph preceding the one you cited:
“We believe that the 2020 election violated Article 1 and 2 of the US Constitution, that various secretaries of state illegally circumvented their state legislatures in conducting their elections in multiple ways, including by allowing ballots to be received after November 3, 2020,” stated a resolution passed on Saturday, the last day of a three-day biennial Texas GOP convention held in Houston, the Texas Tribune reported.
Whether one agrees or not, the resolution frames the absence of repudiation by those other states as lacking dispositive weight. The resolution contends that the certifications by those other states of their own electors' votes were Constitutionally illegitimate - hence, any subsequent failure to repudiate those certifications would be considered similarly illegitimate.
As for the question of Constitutionality (and in this particular case, whether those other states have conformed with the Constitution to the satisfaction of Texas), the states are the ultimate arbiters of what is or is not Constitutional.
[1] The letter of the Constitution may have been observed in the qualification of the certifications of those other states' electoral votes, but that will do nothing to assuage the concerns of those who believe (correctly or incorrectly) that those electoral votes were nevertheless arrived at illegitimately.
[2] They will simply say that the Constitution obviously did not intend that such (allegedly) illegitimate votes be permitted to stand, merely because the legislatures of the relevant states chose to do nothing about it - and that therefore, Texas is not Constitutionally obligated to respect or honor the results.
So far, though, this is just a "resolution" (i.e., just words on paper) issued by a political party in one state, and not an official act (or declaration backed by threat of force) by a state government. So far.
[3]
[1] The fact that, as a practical matter, the United States Supreme Court has historically and routinely been given deference by the states in such matters is to the contrary notwithstanding. Once a sufficient number of states possess the will and wherewithal to deny the Court's putative authority as final arbiter of what is or is not "constitutional" (a power which it was never actually granted, but rather arrogated to itself), then the proverbial gig is up for SCOTUS, except as a mediator of disputes between the states (which is just as it should be, and always should have been - granting,
arguendo, that the Constitution ought even to have been enacted in the first place).
[2] Parliament and the Crown may have observed the letter of British law in the passage and enforcement of the Stamp Act, the Intolerable Acts, etc., for all the difference it made.
[3] Recall that all the inveighing against the Stamp Act, Intolerable Acts, etc. were just so many "resolutions", too - until one day ...
