This is the most likely scenario in my point of view. At times, before one goes to take the decisive action, he or she goes somewhere aside to gather his or her thoughts before going to act. And this might have been the case of Thomas Andrews. I still insist on my opinion of Tommie, as he was called, helping people up until the almost last moment.I have tried to collate information from various sources about Thomas Andrews movements late in the sinking. In one source, probably Geoffrey Marcus' The Maiden Voyage (but I might be wrong), that scene with Andrews standing as if in a daze in the First Class Smoking Lounge when seen by Verandah Steward John Stewart is depicted as taking place quite late in the sinking, at 02:05 am or even later, with his life belt lying on a chair nearby. Also, the painting is described in that source as "Approach to the New World", depicting arrival at New York harbor.
The problem with that conjecture is that Stewart himself was rescued on Lifeboat #15 lowered at 01:40 am, at least 40 minutes before the ship disappeared underwater. So, in OASOG, that scene is calculated to have taken place minutes after Lifeboat #11 was lowered at 01:32 am, with Stewart on his way to the boat deck, which would fit in with the above. Also, the painting above the fireplace in the First Class Smoking Room of the Titanic was "Plymouth Harbour" by Norman Wilkinson; I think that that other painting was in the equivalent place on the Olympic.
In OASOG, Andrews is said to have been seen about half an hour later at around 02:10 am helping to toss deck chairs overboard to help those in the water; moments later he was heading towards the bridge, carrying his life vest. The secondary source of that is author Shan Bullock but apparently the primary source, a survivor, was not mentioned. Soon afterwards Mess Steward Cecil Fitzpatrick was crossing from the lower port side to the starboard side through the bridge and saw Captain Smith and Thomas Andrews in quiet conversation, telling each other that the ship was "going". Fitzpatrick claimed to have "fainted" upon hearing that but he was seen working with other crew in the frantic attempts to launch Collapsible A. Fitzpatrick was one of those flung into the water when Collapsible A floated free and was eventually pulled on board the overturned Collapsible B.
It is believed that Smith and Andrews entered the sea together from the (port side of?) the bridge moments later.