Thank you very much for looking it up. But having seen it, i kind of have bad news...
i've looked that scene in the script, and this is how this particular text is used:
Python:
elif ian_lena_dating:
h "So, about you and Lena..."
h "Is it correct to call you a couple?"
i "What? No, it's not like that..."
i "I mean, we're dating, but we're not a couple. We're just..."
you get this one only when Lena and Ian are
friends with benefits, i.e. they indeed aren't a couple. When Lena and Ian are in committed relationship, this scene plays as follows:
Python:
if ian_lena_couple:
h "So... Lena told me about you two..."
i "She did?"
h "Yeah... I'm happy for you. I think you make for a great couple..."
i "Thanks, Holly. We agreed to take things step by step, though..."
i "I guess not much has changed between Lena and me. I just wanted to be open about my feelings for her."
In other words, on the path where Lena/Ian are an actual couple there's no denial that they're indeed one. Consequently, the expectation to only "experiment together" in such arrangement isn't in any way bullshit, like you originally claimed. On the couple route both Ian and Lena expect their partner to be faithful and don't sleep with other people without getting them also involved. The game supports this approach on mechanics level, tracking instances of sleeping around as cheating, which can eventually cause the relationship to fall apart.