Hello, Thank you for your hint. 
Camino… comes from Catastro Spain. It also uses Catalan like Carrer…, Carretera… and Avinguda…
After checking with the translator, you are right. https://en.pons.com/text-translation/catalan-spanish?q=Cam%C3%AD
Maybe they forgot to translate Camino.

I'm going to correct that in OSM.

There is more information on street names in the Catalan Wiki: https://wiki.openstreetmap.org/wiki/Ca:Illes_Balears#Consells_de_mapeig

The MTN25 Standard also says you're right: https://www.ign.es/web/ign/portal/libros-digitales/toponimia-mtn25
I found the following on page 31 (29 in PDF viewer)(translated to English):

“Examples in non-Spanish-speaking areas:
Camí de Villar del Arzobispo,
Villar del Arzobispo, official name in Castilian
Spanish
but not: Camino de Villar del Arzobispo”

Fun fact on the side: In some places in Dalt Vila and the Santa Eulària des Riu region there are street name signs in Spanish and Catalan.