I can't say from direct experience, but it seems to be the general consensus that the feeding in the enclosure trains them to strike you theory is a myth. Think of it this way, if you only open their enclosure to feed them, it is possible that this could happen, but you will likely be getting into the enclosure to clean, handle, provide fresh water, etc. Your snake is smart enough to know a mouse from your hand as long as you ensure that your hand is not scented. Always wash your hands before reaching into the tank, just in case you smell like something that could be mistaken for prey. Most people actually advise feeding in the enclosure over a separate tub. Bps are sort of notorious for refusing food if any little factor isn't perfect. A tub could easily add enough extra stress that they may refuse food entirely. Basically, feeding in the enclosure gives you the best odds that they will eat. Don't be concerned, just make sure that feeding time isn't the only time that your hand is in the tank.