When connecting to a corporate network, wired or wireless, it's possible for their IT department to intercept your traffic and/or get details of what you're doing on the web -- but in BYOD environments, this possibility can vary greatly. Security varies widely, but there's intrusion detection systems, SSL interception (although this only works from corporate-managed devices), DNS and traffic logs that might reveal what users have been doing on the internet.
Each individual app that you install will have different security standards, depending upon the app vendor's practices. In this case, you identified Grindr in the comments as the app.
A quick web search reveals an evaluation of Grindr security: https://www.os3.nl/_media/reports/grindr.pdf in which you'll find that Grindr does in fact use SSL/TLS for its connection to the Grindr server, where all data is sent/received from (including pictures). Since your smartphone is BYOD, it likely doesn't have corporate master SSL certificates installed. In this case, your employer cannot intercept the SSL traffic. However, if your employer has installed an app to manage your phone or otherwise enforce BYOD policy, this might not be the case. Thus, based on the information you provided, it seems that your connection to Grindr and the data you sent/received is likely secure.
However, your DNS queries and the IPs of the Grindr webservers may be flagged, or website information derived from the SSL certificate exchange before communications are encrypted, so it's possible the employer may (through use of IDS or other sophisticated security apparatuses) know you had been using Grindr, but not what you had sent/received, or what your login information is etc.
So, it may be possible that the corporate network knows you're using Grindr, but likely not your naughty pictures or any other information.
