Hull FC were dominated for 60 minutes by the Tigers in a flat performance from the home team.
A subdued Radford was visibly disappointed with his side’s display after the match.
The coach spoke to the media for just 98 seconds and said: “One team really rolled their sleeves up and turned up with good tempo and another team didn’t, obviously.
“Whether that was a physical thing or a mental thing I don’t know. It might have been a bit of both.
“It’s the third time we’ve played Castleford this year and it’s the third time we’ve played like that, which is disappointing.”
Hull FC rallied in the final quarter to post 16 points, but still ended up 14-point losers.
“I was pleased with the response but I would love to have seen that from the off,” Radford said.
“It was down to our physicality or mental approach and probably in the middle of the field. If you don’t turn up, you get beat.”