The decision was "tough", said Cremer, whose spin bowling had the hosts in early trouble on the final day before a 121- run partnership between Dickwella and Asela Gunaratne secured Sri Lanka's best-ever run chase of 388.
Dickwella rescued Sri Lanka from a precarious 203-5, but the left-handed batsman's gritty 81 needed plenty of luck.
The wicketkeeper-batsman survived a stumping from Sikandar Raza's off-spin on 37 and was then dropped by wicketkeeper Regis Chakabva on 63.
"From what I saw, I honestly didn't see any doubt why it should be not out, but it's just one of those things," Cremer, who led his side to victory in the one-day series, told reporters.
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"I suppose you have technology and it clearly shows ... it's tough when those things go against you when you are trying to win a Test match on the last day," said Cremer who took four for 150.
Gunaratne (80) put on an unbeaten 67-run partnership with Dilruwan Perera (29) to dash Zimbabwe's hopes of a first Test win over Sri Lanka.
"We tried hard. We have missed a few opportunities, but I am very proud about the way the guys played," said Cremer, who got nine wickets in the match including his maiden five-wicket haul in Sri Lanka's first innings.
"To win the ODI series and to push them in the Test match taking it to the last day was a very good effort from the boys.
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