So there was, apparently, reason to think that East held the queen.
West assumed that his partner held the queen, which was certainly possible, and played low.
The play of the club jack would have left the contract in the balance if East had held the queen.
If his partner held the queen, it did not matter.
This play was not going to cost anything, whoever held the queen.
He did not know that his partner held the queen, but it seemed the only hope for the defense.
West now knew that South held the queen, but he did not know whether it was guarded.
Instead he continued with a low heart, in the faint hope that his partner held the queen.
And if East held the queen he would presumably have covered the ten.
The opening lead of the heart eight strongly suggested that East held the queen.