I don't think the experiment design is that weird. This is not the first iDSB system, and the TAM dose was 1.9mg/kg of bodyweight, 2 OOM less than other IDSB papers, administered orally as opposed to intraperitoneally.
And you don't see zero mutagenesis, which I agree would be weird, you see a slight increase in mutagenesis specifically at I-Ppol cut sites, (which are, with a single exception non-coding). I'd have to look at accelerated aging via mutagenesis papers to see exactly how much lower the mutation increase here is vs standard, but I'd expect the rate in this paper to be a lot lower.
Could you be specific about what things, exactly, these results contradict?
I feel as though the existence of "Mucky fat" is a relevant datapoint here
https://www.theguardian.com/lifeandstyle/wordofmouth/2012/feb/22/mucky-fat-butties-sense-place
Though it perhaps says something that this seems to have gotten less popular as food has gotten cheaper