Yes but the description of the function says it filters out strings. So for code re-use it is better to return the list with no strings than it is to return just the integers in the strings. Both will work with the dataset that is given of course. Or you could change the description of what the function does to say it returns only the integers in the string.

Starting at 5 instead of 3

Should really use if clause of generator expression instead of filter:

return {key for key, count in c.items() if count == max}