The unknown here is where the cell was that was producing the lightning.
Judging by the position of CHQ7795 when he returned to land and where BTA1202 was when he diverted, the WX was most likely north of IAD on the final approaches to the 19s.
It would the make sense that BTA decided he could not safely fly the approach to IAD after the lightning strike and diverted to BWI (the 360 was probably needed for ATC coordination) and when CHA turned north on course he got a look at the WX on his route and took a hit then decided to call it a day.
Then WX around here was lousy all day. TRW+ and R+ all day and into the evening. Some places around here got 4 inches of rain.