Both #1 and #6 pistons are at TDC as you state. Both tappets loose on #1 indicates that this cylinder is at the top of the compression stroke. This means that #6 is at the top of the exhaust stroke, which puts the valves in an ‘overlap’ condition. The exhaust valve is closing and the intake valve is opening. Depending on the valve timing of this particular engine the exhaust valve could have just closed, allowing the tappet to be loose, but the intake valve is probably beginning to open, hence the tight tappet.