The work may have been a new card being installed, was your cabinet full already? You can sometimes check and get a rough idea at...
https://www.btwholesale.com/includes/adsl/adsl.htm
Use the postcode and address check and enter just your postcode in both, if it says FTTC is not available, does not have it listed or has an estimate of 0Mb or similar silly figure then it is possible your cabinet was full and they were adding a new card to it.
I regularly check my number to see if the estimate changes (which it has done), however I did also check the address (postcode never lists FTTC however) and both results still say available with no indication that the cabinet was full.