The answer is NO it need not be related in many cases...there are many exceptions as well ...unless u studied medicine,illegal to be a doctor,if not qualified pilot,cant claim it...same for law etc etc..
One way to find out is to check under the noc code in cic site itself
http://www.cic.gc.ca/english/immigrate/skilled/noc.asp
..if it specifies a particular qualification as mandatory,then it might adversely affect.
for 4021,
Employment requirements
- A bachelor's degree, a college diploma or demonstrated expertise in the field of instruction is required.
- A master's degree in the field of instruction may be required.
- A certificate, diploma or degree in adult education may be required.
- For instructors of trades, completion of apprenticeship training and industry or trade certification are required. Additional courses in teaching or a provincial teaching certificate may be required.
unlike in critical profession,i dont think this will be a cause for rejection of application..more likely reason could be claiming an NOC & then the duties and responsibilities not matching with those listed by CIC against that particular NOC...