From the timeline on flightstats, it appears that for some reason they thought they'd have to turn back to SFO, then about fifteen minutes later they changed their minds and continued on to IAH.
Times are PDT:
25 Mar
00:58
Time Adjustment
Estimated Runway Arrival changed from Mar-25-2021 6:01 AM to Mar-25-2021 6:15 AM
Estimated Gate Arrival changed from Mar-25-2021 6:16 AM to Mar-25-2021 6:30 AM
25 Mar
01:03
Status Redirected
Scheduled Runway Arrival changed from Mar-25-2021 5:53 AM
Estimated Runway Arrival changed from Mar-25-2021 6:15 AM
Estimated Gate Arrival changed from Mar-25-2021 6:30 AM
Arrival Gate changed from 19
Arrival Terminal changed from E
Baggage changed from C6
Status changed from Active to Redirected
Redirected/diverted airport changed to SFO
25 Mar
01:12
Gate Adjustment
Departure Gate changed from F12 to E13
25 Mar
01:12
Time Adjustment
Estimated Runway Arrival changed to Mar-25-2021 1:30 AM
Estimated Gate Arrival changed to Mar-25-2021 3:54 AM
Departure Gate changed from E13 to F12
Arrival Gate changed to E13
Arrival Terminal changed to 3
(
https://www.flightstats.com/v2/fligh...tId=1056851413)