That is a good tip for ensuring the bike is upright and center. I assume you hold the clean dipstick cap in place without threading it in, then raise the bike slowly until both centerstand feet touch, while continuing to hold the cap in place, then lean the bike back onto the sidestand. Once again stable on the sidestand, you pull the stick out and check the level. Or do you try to do all the level checking while also holding the bike on a semi deployed centerstand?
Those of us who are less meticulous just check the level with the bike up on the centerstand. It can’t be much different than vertical on both wheels. The reason the Honda oil level spec is given for vertical on both wheels rather than on the centerstand is that the centerstand is an optional accessory not every owner would have.