He drank because it was a training ride and he was not pushing 100 %.Maybe they only did the change after the classics and are still making adjustments.
I'm also assuming that trainning on open roads, where there are cars and you can't ignore traffic rules, makes it hard to go all out, like he would do during the ITT. Maybe he felt it was a good enough setup during trainning.
Honestly, the strangest thing for me was seeing him drink in such a short effort.