From my experience, it is always better to supplement quantitative data with interpretations and understanding of the phenomenon studied. What is your field of the research?
Mixed method is combining quantitative and qualitative methods either sequentially or at the same time. Deciding what method to use is a question you answer at the beginning of your research when you do your research design. But apparently, you have passed that stage. As you already have your data, you cannot be talking of whether you can use mixed method.
What you are probably concerned with now is what to do with the different sets of data you have. That will depend on the nature of the datasets, the objectives and the approach to the study. It seems you want to link the two datasets. In that case, you can do triangulation (of either the data or the results). Triangulation is a procedure that is commonly applied in mixed method research to enable the combination of data and/or results from quantitative and qualitative methods. However, you can apply it in either a quantitative or qualitative research when you have multiple sources of data. It enables you to get consistency across data sources and provides a cross-validation of your results.
'Mixed methods' term is exclusively used for using both qualitative and quantitative data in the same research. It seems that you are using different quantitative methods that would make your study a multimethodology or multimethod research. It should be absolutely OK to use multimethods subject to the condition that you justify it through a unifying theoretical framework.
It is true what @David L Morgan said, I will have multiple quantitative methods in my research (from the questionnaires to manikin data to sensor data etc).
@Marcin Boryczko My field will be nursing, education and emergency care.
I think multimethodology or multimethod research is the answer.