Seirin makes a great needle. It is tough to know for sure without seeing it, but if your technique was sound and location was correct, I’m guessing you may have hit a vascular structure. Often times in this scenario the patient will get more of a sharp sensation, different from the typical deep dull ache you may expect. You also may notice a small amount of bleeding or a small hematoma after needling. If this happens apply immediate manual pressure with a gloved hand or a cotton swab for 5-10 seconds. I have often found that if a patient gets a small hematoma after needling they often have a focused soreness in that spot and occasionally some itching like a bug bite. Let them know this is a typical response and should expect it to clear up in a day or two. One of my favorite things to do if this happens in addition to deep pressure is apply one of those vibration massagers to the area. Seems to help break the tone of the muscle and relieve some of the needle soreness.
If it is the set itself or a superficial tenderness it may be a hypersensitivity of the sensory nociceptors. In the scenario you can try to desensitize the superficial levels with cupping, IASTM, or vibration prior to needling.
Hope this helps.