I was on the bima during the Rabbi's reading of the Megillat Esther this year and was holding one end of the scroll flat. As he advanced through the columns he moved the scroll along and at one stage I let go of my end by accident. The scroll immediately started to roll up but he caught it and we folded it properly again.
When this happened I said 'Sorry' without thinking and then realised I had made a hefsek during the reading.
Afterwards I asked if that counted as a hefsek and was told there is room to be lenient.
My question is how is a hefsek defined in this context? Please supply sources.