Its a muscle, much like a vagina, these things tighten up again in like a day or two. It doesn't indicate experience. The condom thin is also pretty common knowledge. Theres many hotels in asia that you can go to for just a few hours rather than for the night because its meant to be for sex.
Additionally, people in asia tend to live in multigenerational homes. Bringing someone home isnt as common as in western countries, thus couples often go to a hotel. Its kind of common knowledge to plan as such and to expect there to be condoms there.
Just consider when you take a dump. It doesnt permanently grow larger just bc something was moving through it. The misconception that tighter = virgin actually stems from misogynist and patriarchical assumptions about women, and that a 'loose' woman indicates that theyre 'used'. The presence of a hymen tends to exaggerate that. This idea is just portrayed often on yaoi because theres a large female fanbase reading.
But NARRATIVELY, I dont think he did it with the church guy. The MC seems fairly obsessed with the ML, thus it doesnt rly make sense character-wise to do so. Knowledge about sex can come from anywhere on the internet now. Even reading yaoi gives people certain expectations or assumptions about sex.

Anyone else think that MC and the church guy already slept to together? But i think the church guy had told me about being experienced it'll make his future partner very excited.