Hard to tell - the HG may fail when stressed by heat - so did you have a temperature event(s) or losing coolant prior to the "mayo" forming - if so could be leaking coolant hose, a classic failure point being the plastic t -piece behind top left on the RAD or failed water pump.
If no temperature event then some posit that Orange OAT coolant has a weakening effect on the gasket - research the posts on here and draw your own conclusions - I have looked at the debate and as a consequence use non OAT blue coolant in may car for the last 4 years.
