Triangulation is an older term that has been abandoned because it has so many meanings that it is too unclear for careful use. More specifically, the editors of the Journal of Mixed Methods Research have issued a statement that they will no longer consider articles that claim to have used triangulation as their basis.

In contrast, mixed methods simply means a study that combines both qualitative and quantitative methods.

Mixed methods usually refers to using quantitative and qualitative methods simultaneously to address a problem. Triangulation traditionally refers to a qualitative method where you use at least three qualitative sources to triangulate or narrow your results.

James E. McLean The concept of triangulation was originally introduced by Donald Campbell and D. W. Fiske in 1959 as a technique for enhancing the validity of a finding by comparing the results from two different methods that were each designed to answer the same question.

The work you mention was developed by Lincoln and Guba (1985) as a way to enhance the trustworthiness of a qualitative result. FYI triangulation does not require three methods, because the original analogy is to navigation, where the intersection of two lines locates an object at the point of a triangle.

The confusion in mixed methods arose in 1980s and 90s when an alternative version of triangulation arose that "enriched" overall research results through gathering more than one type of data, rather than addressing validity issues by comparing results from alternative methods for answering a shared research question.