Firstly, my pleasure. I am very happy you found my information useful; it also seems to be true.
It seems that the widow living in the house did not want to disclose too much information about the property and probably about other things. It is possible, the family (Aindows) was living in a back room or two; realistically for a strong reason.
Only talking of the past for the reasons above: the census was not only a means of counting how many people were living in a country (town, city etc), but also to collect information about them for official purposes.
Of course, like many industrial towns, there were a large number of immigrants in Wigan due to the growth of industry etc and the need to find employment.
pieman, you stated that: 'The family were known to move about a bit.'
Is it not possible that the family moved address frequently to avoid the authorities?
Why not try to trace the Aindow family tree to an earlier date than 1900. It may be useful to look at the years between 1845 and 1895