Certain consumables, most noticeably canned drinks, when consumed (using right click + "drink") or added to player inventory by double-clicking from the ground/immediate area will be automatically be slotted to the inventory hotbar.
This happens with all canned drinks with the possible exception of SPITE. Seems like SPITE will not always do this. I believe something similar happens when double clicking a weapon spawn to add it to a player's inventory.
Water bottles if consumed from the ground will be taken into hands as is normal, but then they will also be added to the player's inventory if space exists even though only the "drink" action was selected.
This is a minor issue, but maybe points to opportunities for in improvement within the inventory UI code or the canned-drink item code.