take a look at the shadow on his left leg.
also note the tires are 28"
the bars style are more common on ladies bikes.
the chain guard is an accessory one seen on most ladies bikes of the are, same one on the bike in the background.
would make sense if he was older and didnt want to swing his leg around the top tube.
This makes sense that it is a pair of similar or identical ladies' bikes. I see the shadow of a ladies "top" bar there as well. Still looking for a higher-res scan of the picture that includes the second bike.
As for his mobility issues, he was in his early 50s when the photo was taken and he lived to be 76. I'm guessing he was fairly spry at that age, and that the bike was what was available or what someone thought he would need as much as it was actually needed. But who knows - and how can we find out! I'm enjoying the mystery at present but hope there are answers.
As to his visit to Sunny southern California, it seems he was at Cal Tech to confirm that the sun's gravity bent light rays with the help of an astronomer there, and indeed his theory was confirmed, which is one of several good proofs of his general theory of relativity, which we know as "E=MC squared."
While there for the winter quarter of 1931 originally, he returned in 1932 and 1933 for quieter visits. The initial trip was highly public and he met celerities, etc and was photographed extensively. I'm not sure yet when and exactly where the photo was taken but on one of the latter trips he and his wife (who might want a bike too) stayed in a place that was basically a Men's club on the grounds of Cal Tech in Pasedena.
here's a link to the site of the place, called "The Anthenaeum" and built in a Greek revival style, which may or may not be what we see in the background of the photo. Plenty of stuff in California looks Spanish AND mediterranean.... unsure of the source of the various captions that say he is in Santa Barbara for the photo.
https://www.athenaeumcaltech.com/Default.aspx?p=DynamicModule&pageid=342358&ssid=243574&vnf=1
Of the first publicized visit, there is the cute picture of him holding a puppet of himself which was part of a science themed puppet show/ play he attended. And after his first visit and he had returned to Berlin, the great humorist and cowboy philosopher Will Rogers wrote in his daily newspaper column a funny bit that I'll quote here:
"The radios, the banquet tables and the weeklies will never be the same. He came here for a rest and seclusion. He ate with everybody, talked with everybody, posed for everybody that had any film left, at- tended every luncheon, every dinner, every movie open- ing, every marriage and two-thirds of the divorces. In fact, he made himself such a good fellow that nobody had the nerve to ask him what his theory was."