You can also politely but firmly explain to your schooled friend's parents that you understand and respect their decision to send their kids to school, and you'd like that same respect in return. From what you describe, this hasn't been the case.
I was very honest with my daughters about why we chose homeschooling, and often discussed the many benefits we enjoyed. When we return home after a day full of exciting homeschool activities, and my children see the school bus pass by, they are truly grateful for the freedom homeschooling allows them. They have never expressed a desire to spend their days in school.