He didn't want to practice, he wanted to tie her up and have her silent, but he was messing up, and she felt bad for him, she knew there was no danger to her herself, she wanted to get to the bottom of his reason to keep lying.
This may not have sexual intent as service, but it did have it, for people that want to watch this because it has good artwork, great story to tell, and nice character development (for once), they don't need to see this as fan service scene, but for people that look for service scenes in any anime, for those that don't watch anime for the story but for finding and pointing out the fan service as a flaw, this certainly is their proof, for people that see only this in the entire episode, I feel bad for them, spending 23 minutes just for this small bit.
No one mentioned how great Nano was when she jumped in the raging waters to save the idiot writer.
How strange it was that they waited for the poor guy that had to ran after them.
How the landlady agreed with Ohana, surprising probably everyone there.
And how Ohana showed a few of her cards with her understanding her situation and why her own grandmother is treating her for the good of everyone.
And how Minko endured her punishment with dignity, I guess Nano didn't have to, but who knows
