Is the marriage of cricketer Shivam Dube & Anjum Khan legal as per Islamic law even after following Islamic rituals?

Indian cricketer Shivam Dubey got married on July 16. He married his girlfriend Anjum Khan in Mumbai according to Muslim customs. Shivam posted his marriage photographs on his social media profile.
Shivam Dube & Anjum Khan  
According to Islamic law, Shivam should have converted to Islam before marrying Anjum. However, Shivam has not mentioned regarding his conversion to Islam. As a result, their marriage may be called un-Islamic by Islamic religious bodies.
Even Anjum Khan has not mentioned that she accepted the Hindu religion. In their photographs, she has not seen wearing Mangalsutra, an auspicious thread that the groom ties around the bride's neck as per Hindu tradition of marriage.
Ordinarily, the bride accepts the groom's religion and rituals during the marriage, but this has not happened in Shivam and Anjum case. Moreover, Shivam has followed the Islamic ritual without mentioning his conversion to Islam. As a result, Shivam has been criticized by some people belonging to both communities.