They sound young and ignorant. Have a chat with the manager and make some of the points suggested by pps re legal frameworks, infant health and respect for family diversity.
Don't let it influence your relationship with DD re BF or anything else.
I had a similar experience with DD in her first nursery from 6-18 months old. I stuck it for a year because they were kind to DD (even if they thought I was a total oddball) and the nursery was right next door to my office.
Although the staff were never as blatantly rude as with you, it was clear that they regarded my continuing to visit the nursery to BF DD as weird and unnecessary. They blamed this for DD's refusal to eat in the nursery like the other children (most of whom had been fully weaned by the time they started there at 6-12 months). They also implied that DD was too small because of BFing (she's always been 9-15th percentile on the WHO charts) and were surprised that I wasn't supplying any bottles of formula to "bulk her up".
Several staff also made snide comments about DD's cloth nappies (I provided velcro fastening all-in-ones that were no more difficult to use than disposables) and my use of a baby carrier rather than a pram.
No matter how many times I explained that DD would generally refuse to be fed with a spoon but was happy to feed herself, the staff complained at the end of each day that she hadn't eaten anything. It always transpired that they'd tried to spoon-feed her mashed up food rather than leaving her alone with her plate.
Now that she doesn't need to BF in the day, DD is in a new, more open-minded, nursery closer to home. Even though she's still the only baby in cloth nappies, and I'm still the only non-pram-using parent, no one makes a big deal out of it. DD has even begun to eat her lunch at nursery. The difference in attitude is striking.
Having written this, I put up with quite a lot to be able to BF my baby during the day from 6-12 months and spend extra hours with her while commuting.
If you have a choice, explore other nurseries too.