>I say size was statistically significant not quality of data

Size is not necessarily significant unless is a random selected sample (and I'm not sure volunteers would count as random).

Let's say you have a population of 100 and there are two groups (A-80% and B- 20%). Let's say that individuals in group A are more keen to voluteer themselves. You could have a sample of 50% of the population and still not have a representative sample of their entire population (ie. 49 from A and 1 from B), so the sample size didn't matter to much in that case.