Miguel had expected the pause. This was all new and weird for Sarah, which he more than understood - he'd gone through this same sort of weirdness, after all. So he didn't press for anything until she responded and started to kiss back. And then he simply proved that he knew it was still her, even if she was male and taller than him and had a beard, and kissed her as if she was still in her female body. After all, Sarah had no problem with kissing him (or anything else) when he was female. It would be pretty shocking awful of him to say "Thanks, but no thanks" just because of something that wasn't her fault.
So he kissed her, pulling her in as close as he could get her and bringing the hand that had been on her back up to tangle in her hair even if it was shorter than either of them were used to, and all the angles were different. It was Sarah, he loved her no matter what, and he was determined to let her know.