I faced a few teams like that last year when I was in Marshes to Estate. @DinoTyrant is correct. I believe they are players who are trying to get easy matchups and high trophy scores due to their level 1 dinos.
They can easily wipe your team with their high level boosted dinos if they get even 1 of them. They are gambling of course as they are majorly screwed if all 4 are their lowest dinos.
Most of us now in high Aviary-low Library will face the more painful variant of this tactic. Super boosted steroid high/max level Thors, Indo G1, Erlidom,
etc and the rest are only L21 unboosted. You lose 3-0, 3-1 and yet lose 36-40 trophies!
Very frustrating, and a reason why many have stopped arena battling. Me, I do enough to just get my daily and follow the best advise I got: Stop after losing 3 straight. Wait 30 min to 1 hr and then come back when those mutants have moved up.