This is a good point, and something that could be a possibility. The friend , who I have seen on fb groups, but not commenting on that day, was at home and going to hospital for an op later that day. TM says the friend was nervous so he visited him, and then when the friend left for the hospital, TM fell asleep at the friends house. So he, TM ,says he didnt leave Gordon all that day.
So we really only have his word of why he didn't go shopping, and what he did after his friend left, assuming he did visit with him.
Its possible he stayed behind for another reason, knowingly or not