The problem is that this spam check checks also hikashop registrations.
There are 3 solutions:
1. modify that spam check to not check registrations coming from HikaShop.
2. modify that spam check to also be displayed on HikaShop's registration page.
3. use another spam check which works for both registration pages. For example, you have that plugin:
extensions.joomla.org/extensions/access-.../authentication/7319
It checks on registration without a question by analyzing the data of the registration against online databases of spam and other things.
For both 1 and 2 solutions, you should ask the developer of the spam check.